In the manufacture of semiconductor integrated circuits (IC), dielectric materials such as silicon dioxide (SiO2), silicon nitride (Si3N4), and silicon oxynitride (SiON) have been widely used as insulators for transistor gates. Such insulators are often called gate dielectrics. As IC device geometry shrinks, gate dielectric layers have become progressively thinner. When the gate dielectric layer approaches thicknesses of a few nanometers or less, conventional SiO2, Si3N4, and SiON materials undergo electric breakdown and no longer provide insulation. To maintain adequate breakdown voltage at very small thickness (≦10 nm), high dielectric constant materials can be used as the gate insulating layer. The term “high dielectric constant materials”, as used herein, describe materials where the dielectric constant is greater than about 4.1, or the dielectric constant of silicon dioxide. In addition, high dielectric constant materials can also be used as the barrier layer in deep trench capacitors for semiconductor memory chip manufacturing. The IC industry has experimented with many high dielectric constant materials. The latest and most promising high dielectric constant materials are metal oxides such as Al2O3, HfO2, ZrO2, and mixtures thereof, and metal silicates such as HfSixOy, ZrSixOy, and mixtures thereof. In some instances, nitrogen may be incorporated into these metal oxides and metal silicates high dielectric constant materials (such as HfSiON or AlSiON) to improve the dielectric constant and to suppress crystallization of high dielectric constant materials. For example, crystallization of high dielectric constant materials such as HfO2 causes high leakage current and device failure. Therefore, incorporation of nitrogen can dramatically improve the device reliability. In other instances laminate structures of two or more of the above mentioned materials are deposited as the high k dielectric layer. For example, a laminate structure of Al2O3 followed by HfO2 is being employed as the barrier layer in deep trench capacitors.
High dielectric constant materials such as Al2O3, HfO2, and ZrO2 are very stable and resistive against most of the etching reactions, which has led to their use as etch stop layers and hard mask layers in plasma etching of other materials. See, e.g., K. K. Shih et al., “Hafnium dioxide etch-stop layer for phase-shifting masks”, J. Vac. Sci. Technol. B 11(6), pp. 2130–2131 (1993); J. A. Britten, et al., “Etch-stop characteristics of Sc2O3 and HfO2 films for multilayer dielectric grating applications”, J. Vac. Sci. Technol. A 14(5), pp. 2973–2975 (1996); J. Hong et al., “Comparison of Cl2 and F2 based chemistries for the inductively coupled plasma etching of NiMnSb thin films”, J. Vac. Sci. Technol. A 17(4), pp. 1326–1330 (1999); U.S. Pat. No. 5,972,722 to Visokay et al.; U.S. Pat. No. 6,211,035 B1 to Moise et al., U.S. Patent Application Publication US2001/0055852 A1 to Moise et al.; and EP 1,001,459 A2 to Moise et al.
These high dielectric constant materials are typically deposited from chemical precursors that react in a deposition chamber to form films in a chemical vapor deposition (CVD) process. In some instances, these high dielectric constant materials are deposited onto semiconductor substrates (wafers) by atomic layer deposition (ALD), in which the films are deposited in controlled, nearly monoatomic layers. Apparatus and processes for performing ALD are disclosed in, e.g., U.S. Pat. No. 5,879,459 to Gadgil et al., U.S. Pat. No. 6,174,377 B1 to Doering et al., U.S. Patent Application Publication US2001/0011526 A1 to Doering et al., U.S. Pat. No. 6,387,185 B2 to Doering et al., WO 00/40772 to Doering et al. and WO 00/79019 A1 to Gadgil et al. This family of patents assigned to Genus, Inc. teach that “In situ plasma cleans allow the realization of a very long time between maintenance cleaning.” (See, e.g., U.S. Pat. No. 6,387,185 B2 at column 7, lines 27–28.) However, no details of any process for plasma cleaning of ALD chambers were given in the above family of disclosures.
Plasma sources have been used to enhance atomic layer deposition processes (PE-ALD). For example, Pomarede et al. in WO 02/43115 A2 teach the use of plasma sources to generate excited reactive species that prepare/activate the substrate surface to facilitate subsequent ALD. Nguyen et al. in WO 02/43114 A2 teach the use of a pulsing plasma to enact ALD processes instead of alternating precursor chemical flows. Again, these publications do not disclose any method to clean the ALD residues after the wafers have been processed.
While the deposition process desirably generates high dielectric constant films on a substrate (typically a silicon wafer), the reactions that form these films also occur non-productively on other exposed surfaces inside of the deposition chamber. Accumulation of deposition residues results in particle shedding, degradation of deposition uniformity, and processing drifts. These effects can lead to wafer defects and subsequent device failure. Therefore, all CVD chambers, and specifically ALD chambers, must be periodically cleaned.
Various references discuss adding certain compounds to the plasma in order to effect the etch rate of Al2O3. The references, W. G. M. Van Den Hoek, “The Etch Mechanism for Al2O3 in Fluorine and Chlorine Based RF Dry Etch Plasmas”. Met. Res. Soc. Symp. Proc. Vol. 68 (1986), pp. 71–78 and Heiman, et al., “High Rate Reactive Ion Etching of Al2O3 and Si”, J. Vac. Sci. Tech., 17(3), May/June 1980, pp. 731–34, disclose adding a fluorine based gas or a chlorine based gas, respectively, to an Ar plasma to increase the etch rate of Al2O3. However, these studies were all under the reactive ion etch (RIE) conditions. Ion bombardment/sputter induced reactions play a much large role than chemical etching reactions. Like other prior arts, such extreme RIE conditions do not apply to cleaning grounded chamber surfaces.
In view of the dearth of art disclosing methods for removing high dielectric constant residues, ALD and CVD reactors have typically been cleaned by mechanical means (scrubbing or blasting) to clean up the deposition residues from the internal surfaces of the chamber and downstream equipment (e.g. pump headers and exhaust manifolds). However, mechanical cleaning methods are time-consuming, labor-intensive, and damaging to the surfaces being cleaned.
Other than using mechanical means (scrubbing or blasting) and/or wet chemicals to clean up the deposition residues from the internal surfaces of the chamber, a dry-cleaning process has been developed by using a Cl-containing reactive agent, where BCl3 is one of the preferred Cl-containing compounds. It is believed that BCl3 is a particularly effective cleaning agent for removing high dielectric constant deposition residues due to two synergistic chemical mechanisms. First, boron atoms may act as an oxygen scavenger to assist in breaking the metal-oxygen bonds. Second, chlorine atoms can react with the metal atoms to form species that are more volatile than the corresponding metal oxides. Even though this process can effectively remove the high dielectric constant material residues inside the chamber, it can also generate boron-containing solid byproducts, such as B2O3. Boron residues can act as a p-type dopant and may cause contaminations problems to integrated circuits. Further, its deposition on the vacuum lines can also cause vacuum equipment failure. Thus, the removal of the boron-containing residues is necessary to ensure product quality and equipment integrity.
Fluorine-containing plasma-based processes (i.e., dry cleaning) are commonly used to remove residues of silicon compounds (such as polycrystalline silicon, SiO2, SiON, and Si3N4) and tungsten from the interior surfaces of chemical vapor deposition (CVD) reactors. In these processes, fluorine reacts with the aforementioned residues to produce, for example, SiF4 or WF6, volatile species that can be pumped out of the reactor during the cleaning process. However, fluorine-based chemistry alone is ineffective in removing the high dielectric constant materials discussed above. See, e.g., J. Hong et al., J. Vac. Sci. Technol. A, Vol. 17, pp 1326–1330, 1999, wherein the authors exposed Al2O3 coated wafers to NF3/Ar based inductively coupled plasmas, and found that “the greater concentration of atomic F available at high source power contributed to thicker fluorinated surfaces, leading to the net deposition rather than etching.” In the case of high dielectric constant materials the metal fluoride product that forms is nonvolatile and, thus, difficult to remove from the reactor.
Thus, there is an urgent need for a process to chemically dry clean high dielectric constant material residues, such as Al2O3, HfO2, ZrO2, HfSixOy, ZrSixOy and mixtures thereof, residues of laminates containing high dielectric constant materials such as HfO2 and Al2O3 (also referred to as HfAlO), and residues from nitrogen containing high dielectric constant materials such as HfON, AlON, and laminated materials between HfON and AlON (HfAlON), from ALD reactors without venting/opening up the reactor. An effective chemical dry cleaning method will significantly increase the productivity and lower the cost-of-ownership (CoO) for ALD-based deposition processes.
All references cited herein are incorporated herein by reference in their entireties.